So far, so good. However, I cannot write to the mounted directory. I can, however, read files with permissions -rw-------. The only answer to this question says "It does seem that rpc.idmapd doesn't support ID to name mapping that would let you make changes to the file system". But it doesn't give reference, and I'm not yet prepared to believe that NFS4 is so badly designed that Kerberos is necessary for such a frequent use case.